Metal nano-objects, formed on semiconductor surfaces, and method for making said nano-objects

ABSTRACT

Metallic nano-objects, formed on surfaces of semiconductors, and a process for manufacturing these nano-objects.  
     The invention is applicable in nano-electronics and for example provides a means of obtaining nano-objects ( 4 ) by depositing a metal on a prepared surface ( 2 ) of cubic SiC.

TECHNICAL DOMAIN

This invention relates to metallic nano-objects formed on the surfacesof a semiconductor and more particularly a semiconductor with a largegap, in other words with a large forbidden band width, and a process formanufacturing these nano-objects.

More particularly, the invention relates to metallic nano-objects, forexample such as atomic threads, single dimensional nano-structures andmetallic quantum dots, particularly formed on silicon carbide surfaces,and a process for manufacturing such nano-objects.

The invention is particularly applicable to the nano-electronics field.

STATE OF PRIOR ART

Nano-objects are manufactured by auto-organisation, particularly at orabove room temperature, without individual manipulation of atoms,particularly by near field microscopy, which is usually done cold (usingliquid nitrogen or liquid helium) to prevent migration of atoms (seedocuments [7] to [9] mentioned below).

Further information about surface treatment (particularly semiconductingsurfaces) and the manufacture of nanostructures, and particularlysingle-dimensional nanostructures, can be obtained in the followingdocuments:

[1]. Electronic promotion of silicon nitridation by alkali metals.

P. Soukiassian, H. M. Bakshi, H. I. Stamberg, Z. Hurych, T. Gentle andK. P. Schuette Physical Review Letters 59, 1488 (1987)

[2]. CH₃CI adsorption on a Si(100)2×1 surface modified by an alkalimetal over layer studied by photoemission using synchrotron radiation

T. M. Gentle, P. Soukiassian, K. P. Schuette, M. H. Bakshi and Z. Hurych

Surface Science Letters 202, L 568 (1988)

[3]. Nitridation of silicon and other semiconductors using alkali metalcatalysts

P. Soukiassian

U.S. Pat. No. 4,735,921 A

-   [4]. Process of depositing an alkali metal layer onto the surface of    an oxide superconductor

P. Soukiassian and R. V. Kasowski

U.S. Pat. No. 4,900,710 A

[5]. Fils atomiques de grande longueur et de grande stabilité, procédéde fabrication de ces fils, application en nanoélectronique

G. Dujardin, A. Mayne, F. Semond and P. Soukiassian

French patent application No. 96 15435, Dec. 16, 1996 (see also U.S.Pat. No. 6,274,234 A)

[6]. Couche monoatomique de grande taille, en carbone de type diamant,et procédé defabrication de cette couche

V. Derycke, G. Dujardin, A. Mayne and P. Soukiassian

French patent application No. 98 15218, Dec. 2, 1998

[7]. L. J. Whitman, J. A. Stroscio, R. A. Dragoset and R. J. Celotta,Science 251, 1206 (1991)

[8]. T. C. Shen, C. Wang, G. C. Abaln, J. R. Tacker, J. W. Lyding, Ph.Avouris and R. E. Walkup, Science 268, 1590 (1995)

[9]. M. F. Crommie, C. P. Lutz, D. M. Eigler and E. J. Heller, Surf.Rev. Lett. 2, 127 (1995)

PRESENTATION OF THE INVENTION

This invention proposes metallic nano-objects such as atomic threads,single-dimensional nanostructures and metallic quantum dots, that can bevery useful in the nano-electronics and opto-electronics fields.

The invention also solves the problem of manufacturing such nano-objectson the surface of a large gap semiconductor, particularly siliconcarbide.

This is an auto-organised fabrication on this surface.

Candidate substrates for such organisation are substrates for which thesurface diffusion barrier is anisotropic as a function of a parametersuch as the temperature, a mechanical stress, etc.

Nano-objects are made by controlling the very delicate balance betweenadsorbate-adsorbate and adsorbate-substrate interactions (the adsorbatebeing the metal) and controlling the metal atom diffusion barrier.

In one particularly advantageous embodiment, the invention is used toobtain atomic threads and nano-structures of a metal, particularlysilver, along a direction perpendicular to the direction of the atomiclines or atomic threads made of silicon that were previously formed onthe surface of a silicon carbide substrate.

Specifically, this invention relates firstly to a set of nano-objects,particularly atomic threads, single dimensional nano-structures andquantum dots, this set being characterised in that the nano-objects aremade of a metal and are formed on the surface of a substrate made of amonocrystalline semiconducting material.

This monocrystalline semiconducting material may be chosen from amongmonocrystalline silicon carbide, monocrystalline diamond, covalentmonocrystalline semiconductors, and composite monocrystallinesemiconductors.

This substrate may be a monocrystalline substrate of silicon carbide inthe cubic phase.

According to one particular embodiment of the set according to theinvention, the surface is a cubic silicon carbide surface, rich in β-SiC(100) 3×2 silicon.

Then nano-objects may be three-dimensional clusters of the metal on thesurface.

According to one advantageous embodiment of the invention, the clustersare distributed in an orderly manner on the surface and thus form alattice of metal dots.

According to another particular embodiment, the surface is a cubicsilicon carbide surface which is Si terminated, β-SiC(100) c(4×2) andthe nano-objects are parallel atomic threads or parallelsingle-dimensional nanometric strips of the metal.

The surface may comprise parallel atomic threads of Si, the atomicthreads and single-dimensional strips of the metal being perpendicularto these atomic threads of Si.

The surface may comprise passivated areas and non-passivated areas, thenano-objects being formed on these non-passivated areas of the surface.

This invention also relates to a process of making a set of nano-objectsin which a surface of a substrate made of a monocrystallinesemiconducting material is prepared, and a metal is deposited on thesurface thus prepared.

This monocrystalline semiconducting material may be chosen from amongmonocrystalline silicon carbide, monocrystalline diamond, covalentmonocrystalline semiconductors and monocrystalline compositesemiconductors.

This substrate may be a monocrystalline substrate of silicon carbide inthe cubic phase.

The metal may be deposited at a temperature greater than roomtemperature.

According to a first particular embodiment of the process according tothe invention, a surface of cubic silicon carbide rich in siliconβ-SiC(100) 3×2 is prepared, and the metal is deposited on the surfacethus prepared.

According to a second particular embodiment, a silicon carbide surfacewhich is Si terminated β-SiC(100) c(4×2) is prepared. The metal isdeposited at room temperature on the surface thus prepared and, bysurface migration of metal atoms along lines of Si—Si dimers of thesurface c(4×2), one obtains atomic threads of the metal that areparallel to the lines of Si—Si dimers or silicon threads.

A thermal annealing of the substrate can then be carried out at atemperature below the total desorption temperature of the metal.

The result obtained is atomic threads parallel to each other orsingle-dimensional nanometric strips parallel to each other, of themetal on the surface. Thus, these atomic threads and thesesingle-dimensional strips of the metal, thus prepared at a highertemperature, are perpendicular to the atomic threads of Si.

The metal may be deposited by evaporation in vacuum or in an inertatmosphere.

Passivated areas can be formed on the prepared surface and the metal canthen be deposited on non-passivated areas of this surface.

In this invention, the metal may be chosen from among metals for whichthe d band is full, jellium type metals, alkaline metals (particularlysodium and potassium) and transition metals.

Instead of using a thermal annealing, a laser can be used to obtaindesorption of metal either by thermal interaction of the beam emitted bythis laser over the surface covered with metal, or by desorption of themetal induced by electronic transitions (DIET).

In the process according to the invention, the surface may be an sp typeC terminated surface, namely the β-SiC(100) c(2×2) surface.

This surface may comprise atomic lines of sp3 type C.

According to the invention, we can then form atomic threads of the metalthat are either parallel or perpendicular to the atomic lines of C.

According to one particular embodiment of the invention, a lattice ofmetal dots is formed on the surface of the substrate made ofmonocrystalline semiconducting material, the substrate material locatedunder the dots is locally transformed and the lattice of dots iseliminated to thus obtain a super-lattice of dots made of thetransformed material.

Preferably, the local transformation of the substrate material is chosenfrom among oxidation, nitridation and oxynitridation to obtain asuper-lattice of dots made of the oxide, nitride or oxynitride of thematerial.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be better understood after reading the descriptionof example embodiments given below purely for guidance, and in no waylimitative, with reference to the appended figures, wherein:

FIG. 1 is a diagrammatic view of three-dimensional metallic clustersobtained according to the invention,

FIG. 2 is a diagrammatic top view of metallic atomic threads obtained onaccordance with the invention and parallel to the atomic lines of Si,

FIG. 3 is a diagrammatic top view of metallic atomic threads andsingle-dimensional strips obtained according to the invention andperpendicular to the atomic lines of Si,

FIG. 4 is a diagrammatic top view of such atomic threads andsingle-dimensional strips obtained according to the invention, onnon-passivated areas of a silicon carbide surface,

FIG. 5 shows a diagrammatic view of a lattice of sodium clustersobtained in accordance with the invention on an SiC substrate,

FIG. 6 shows a diagrammatic sectional view of this substrate, carrying asuper-lattice of silica dots obtained by a process according to theinvention, and

FIG. 7 shows LEED photographs of a clean surface β-SiC(100) 3×2 (A), ofthe same surface covered by Na clusters and organised into a 3×1 lattice(B) and of the same surface covered by Na clusters and organised into a3×2 lattice (C).

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

We will now give a first example of the process according to theinvention, used to manufacture silver clusters.

We start by preparing a cubic silicon carbide surface, rich in siliconβ-SiC(100) 3×2, in other words a plane surface of silicon carbide SiC inthe β-SiC(100) cubic phase, rich in silicon and with a 3×2 surfacereconstruction.

This type of preparation is described in various documents mentionedabove, particularly document [5] to which we will refer.

A small quantity of silver is deposited by vacuum evaporation onto thissurface rich in Si and with a 3×2 structure, for example starting from asilver source arranged facing the surface and heated by a tungstenfilament.

By forming an image of the surface by STM or Scanning TunnellingMicroscopy, it is observed that silver does not wet the surface andforms three-dimensional clusters with a size varying from 0.9 nm to 3nm, and therefore capable of forming quantum dots.

The number, size and spacing of these clusters or islands can vary as afunction of the quantity of silver deposited and annealing temperatures.This growth mode indicates dominant interaction between silver atoms.

FIG. 1 shows a diagrammatic top view of the surface 2 on which theclusters 4 are formed.

For information purposes only and in no way limitatively, the silverdeposit takes place in a chamber in which the pressure is less than2×10⁻⁸ Pa and for example is equal to 6×10⁻⁹ Pa; the distance betweenthe surface and the silver source is equal to about 15 cm; the currentpassing through the silver source throughout deposition is equal to 4 A;the deposition time is between 2 minutes and 8 minutes (8 minutescorresponding approximately to a single layer of silver); the depositiontakes place leaving the SiC sample at room temperature (about 20° C.).The necessary annealing operations are done at about 500° C. Theannealing temperature can be varied to adjust the migration velocity ofmetal atoms (the migration velocity increases with the temperature) andthe quantity of desorbed metal (that increases with the temperature),and therefore to vary the size and spacing of the clusters.

Note that silver evaporates completely during a short annealing at about700° C. for a few tens of seconds.

We will now give a second example of the process according to theinvention which makes it possible to manufacture single dimensionalstrips of silver or silver threads.

We will start by preparing a cubic silicon carbide surface which is Siterminated β-SiC(100) c(4×2), in other words a surface of SiC inβ-SiC(100) cubic phase, this surface being Si terminated and c(4×2)reconstructed.

Furthermore, parallel auto-organised atomic lines of silicon rest onthis surface, these lines forming lines of Si—Si dimers.

Refer to document [5] which explains how straight lines of Si—Si dimers(atomic lines) are obtained on the surface of a monocrystallinesubstrate of SiC in the β-SiC(100) cubic phase that is transformed sothat its surface is 3×2 terminated and that is then suitably annealed.

Thus, this 3×2 symmetry surface is transformed by thermal annealings at1100° C. until it has an atomic scale organisation (reconstruction) withc(4×2) symmetry.

Silver is deposited on the β-SiC(100) c(4×2) Si surface thus obtained,under the same conditions as in the first example.

It is found that at room temperature, the silver atoms diffuse on thesurface slowly, along the lines of dimers, giving metal atomic threadsparallel to these lines.

FIG. 2 shows a diagrammatic top view of the surface 6 supporting theparallel lines 8 of Si—Si dimers and the atomic threads of metal 9 thatare parallel to these lines.

When the surface is covered with silver, annealing is done below thetotal desorption temperature of silver (700° C.).

The silver layer is selectively desorbed and atoms remaining on thesurface are organised to make single dimensional nanometric parallelstrips of silver, or parallel atomic threads of silver. The direction ofthese atomic threads and these single-dimensional strips isperpendicular to the lines of dimers.

FIG. 3 shows a diagrammatic top view of the surface 6 supporting theparallel lines 8 of Si—Si dimers and the atomic threads of silver 10together with the single-dimensional nanometric strips of silver 12.

For guidance purposes only and in no way limitatively, in the secondexample the silver deposition takes place in a chamber at a pressureequal to 2.1×10⁻⁹ Pa; silver is deposited for 8 minutes using a silversource through which a 4 A current passes; the sample is left at roomtemperature during the silver deposition; after the deposition, thesample is annealed by passing a current of 0.5 A through it for 5minutes.

Consequently, silver threads can be constructed perpendicular to theatomic threads of Si (see document [5]).

This is extremely important for building up artificial lattices at asub-nanometric scale, that can be very useful in nano-electronics.

We can replace silver by other metals with a full d band, such as goldor copper, or by jellium type metals such as aluminium.

Remember that a jellium type metal is a metal for which electron gas isfairly homogenous and for which positive ionic charges are largelysmeared within the entire volume of the metal to give a positive anduniform background.

Silver can also be replaced by transition metals, for example such asMo, W, Ta, Nb, Co, Fe, Mn, Cr, Ti.

With metals with magnetic characteristics, the invention can be used todope or manufacture nanostructures, for example with magnetic propertiesthat are attractive in spin electronics.

Silver can also be replaced by other metals such as alkaline metals thatare remarkable catalysts for surface reactions with organic or inorganicmolecules (see documents [1] and [2]).

Therefore, reactions on the atomic scale can be provoked and a verylocalised passivation, for example by oxidation, nitridation oroxynitridation, or a manufacturing of silicones at atomic or molecularscales can be encouraged.

Alkaline metals also have the remarkable property of considerablyreducing the electron work function, and reaching the negativeelectro-affinity condition, in other words forming natural electronemitters. This invention enables this emission to take place startingfrom nanostructures of alkaline metals (for example Cs, Rb, K or Na).

Instead of using vacuum evaporation to deposit metal, this evaporationcan be done at a higher pressure, in an inert atmosphere (rare gas,etc.).

Concerning the second example, note that the process according to theinvention can be used to selectively control migration or desorption ofatoms of the metal (for example silver) by varying the temperature. Avariation of the temperature acts on the movement of Si—Si dimers on SiCor provokes this movement.

In a variant of this second example, the surface of cubic SiC, Siterminated β-SiC(100) c(4×2) is prepared without atomic lines ofsilicon, metal is deposited and annealing is carried out at atemperature below the total metal desorption temperature.

As before, one thus obtains atomic threads of the metal and/orsingle-dimensional nanometric strips of this metal. These atomic threadsand these single dimensional strips are parallel to each other and areperpendicular to the direction along which parallel lines of Si—Sidimers would be formed.

In another example of the invention, a prepared surface of a cubic SiCsample is locally passivated using hydrogen and the atomic threadsand/or single dimensional strips of the metal are formed in thenon-passivated areas.

FIG. 4 is a diagrammatic top view of the locally passivated surface 14thus comprising passivated areas such as area 15 and non-passivatedareas 16 and 18. The parallel atomic lines of silicon that are presentin these areas 16 and 18 are marked with reference 20. Atomic threads 22of metal and single-dimensional strips 24 of this metal can also beseen, formed in these areas perpendicular to the lines 20.

In order to locally passivate the surface, areas that are not to bepassivated are covered by a photoresist layer, and this photoresistlayer is eliminated after passivation of uncovered areas.

If the direction of lines of Si—Si dimers is known in advance,non-passivated rectangular areas can be formed with one of their sidesparallel to this direction.

To passivate the cubic SiC surface using hydrogen, this surface isprepared so as to have a controlled organisation with c(4×2) symmetry atatomic scale. This surface is then exposed to molecular hydrogen untilsaturation. The SiC is kept at room temperature during exposure tomolecular hydrogen.

For example, cubic SiC is placed in a treatment chamber in which thepressure is kept at less than 5×10⁻¹⁰ hPa, and is heated by passing anelectrical current directly in this SiC substrate. The substrate isheated to 650° C. for several hours and then increased to 1100° C. forone minute several times.

By means of a silicon source heated to 1300° C. several single layers ofsilicon are deposited on the (100) surface of the cubic SiC.

By means of thermal annealing at 1000° C. some of the deposited siliconis evaporated in a controlled manner until the surface has anorganisation at the atomic scale (reconstruction) with 3×2 symmetry.This surface symmetry may be controlled by electron diffraction.

Thermal annealings at 1100° C. are applied to transform the surface with3×2 symmetry until it has an organisation at the atomic scale(reconstruction) with c(4×2) symmetry.

This surface is then exposed to ultra pure molecular hydrogen at lowpressure (10⁻⁸ hPa).

The surface is kept at room temperature during this exposure.

The SiC surface is exposed until saturation (more than 50 L).

This saturation may be controlled by a scanning tunnelling microscope orby a valence band photoemission technique.

Instead of using an Si terminated surface, all the processes describedabove may also be used on an sp type C terminated surface, theβ-SiC(O)c(2×2) surface that may itself include sp3 type atomic lines ofC (see document [6]).

According to the invention, we can thus form atomic threads of metalthat are either parallel or perpendicular to the atomic lines of carbon.

In the following, we will consider other examples of this invention,namely:

-   -   obtaining sodium clusters on the surface of a semiconducting        substrate, particularly a monocrystalline substrate of silicon        carbide in the cubic phase,    -   more particularly, obtaining this type of cluster distributed in        an orderly manner on the surface of this substrate and thus        forming a super-lattice of sodium dots, of the type of the set        of clusters in FIG. 1 in which the distribution of clusters is        substantially regular; and    -   obtaining a super-lattice of silica dots on the substrate        (remember that we have already given examples of the invention        in the above, for local passivation using alkaline metals).

The sodium deposit on β-SiC(100) 3×2, which is the Si rich surface ofcubic silicon carbide, has been studied. Unlike the case of the Siterminated β-SiC(100) c(4×2) surface on which Na and other alkalinemetals are adsorbed in the form of a metallic film with a thicknessapproximately equal to the size of an atom, in this case Na is adsorbedin the form of spherical shaped metallic clusters, which isunprecedented for an alkaline metal on the surface of a semiconductor:this does not occur on the corresponding surfaces of silicon orconventional III-V composite semiconductors (therefore not includingIII-V nitrides). This means that the adsorbate-adsorbate interaction onthis Si rich surface is more important than the adsorbate-substrateinteraction. This behaviour should be compared with the behaviour ofsilver on the same surface (see above).

Na clusters are identified by means of a plasmon at 3.1 eV correspondingexactly to the energy of Na spherical clusters. Results also suggestthat sodium clusters are regularly spaced and that their size tends toreduce when their coverage ratio increases. Indeed for the thickestdeposits (from approximately one atomic single layer up to severalatomic single layers) and after progressive annealings up to 350° C.,the slow electron diffraction diagram becomes very contrasted, thusshowing that Na clusters are well organised and regularly spaced on theβ-SiC(100) 3×2 surface. We have made photographs of the sodium clusterson β-SiC(100) 3×2 by LEED, in other words by low energy electrondiffraction. These photographs show that these Na clusters are wellordered and regularly spaced, with different orders and thereforedifferent spacings as a function of the surface coverage ratio. Refer tothe photographs in FIG. 7.

We thus form auto-organised quantum dots of Na by varying theequilibrium between adsorbate-adsorbate and adsorbate-substrateinteractions, by controlling the temperature and quantity of metaldeposited. This result is very important and the dots obtained are verysignificantly different from other quantum dots due to the intrinsicproperties of alkaline metals such as sodium.

On one hand, these dots are made on the surface of a semiconductor,which is unprecedented, and moreover it is a wide gap semiconductor.

On the other hand, alkaline metals such as Na have a very lowelectroaffinity. They reduce the work function of the surfaceconsiderably, by several electron-volts, and it is possible to obtain anegative electroaffinity condition, in other words a natural electronemitter (with the surface only or exposed to oxygen), or a photoelectronemitter when the system is exposed to light. A similar phenomenon isused for manufacturing of light amplifiers in night vision devicesstarting from gallium arsenide surfaces covered with Cs and oxygen.

The importance of the result mentioned above (obtaining a lattice ofquantum dots of Na) is due to the fact that a lattice of Na dots(clusters) 26 is available (see FIG. 5), with nanometric orsub-nanometric size, that are regularly distributed on the surface of asubstrate 28 made of a semiconducting material with a large gap andleave the exposed SiC surface between them.

Therefore, these dots can emit electrons under the effect of a biasingvoltage or under the influence of light. This makes it possible to formactive matrices for the manufacture of flat screens.

Another important characteristic of alkaline metals, particularlysodium, is due to their exceptional properties as catalysts foroxidation, nitridation, oxynitridation and reaction with organicmolecules.

These properties have been demonstrated during work on silicon, III-Vsemiconductors, metals such as aluminium, and SiC. Refer to documents[10] to [23] mentioned at the end of this description, and to documents[3] and [4] mentioned above.

This opens up a very broad new field of applications that can be called“nano-lithography” or “nano-fabrication”. Due to these Na dots, exposureto oxygen (respectively nitrogen) can result in a localised oxidation or(respectively nitridation) of part of the SiC substrate 28 (see FIG. 6),that is located below each Na cluster, then each of these clusters 26can be eliminated by a thermal desorption at low temperature (about 650°C.). The result is a super-lattice of SiO₂ (respectively Si₃N₄) dots atnanometric scale.

Similarly, a localised oxynitridation of this part of the SiC substratecan be achieved by exposing the surface covered by Na clusters to NO orN₂O (exposures with low quantities, typically of the order of a fewlangmuirs), and clusters can then be eliminated by thermal desorption byapplying the Na desorption temperature on the substrate considered.

Similarly, with organic molecules, for example CH₃Cl molecules,nanometric silicone dots can be manufactured and other molecules can beused to make other dots such as polymer dots and metalorganic dots: thesurface can be exposed to the molecules to obtain silicone dots orpolymer dots or metalorganic dots under each of the sodium dots, and thesodium dots can then be eliminated.

The polymer dots (respectively metalorganic dots) mentioned above canalso be used as anchor points on the surface on which they are formed,for the molecules used to form these dots.

Finally, the Na—Na interaction can be controlled/optimised by exposingthe surface provided with Na dots to small quantities (approximately theorder of one langmuir) of inorganic or organic molecules (for examplehydrogen, oxygen or any other molecule or element known to those skilledin the art as being capable of interacting with Na or alkaline metals).This will lead to the formation of larger Na clusters.

We will now explain how to obtain sodium quantum dots.

Concerning the preparation of a sample with a β-SiC(100) 3×2 surface wewill refer particularly to document [5].

A sample prepared in this way is then placed in a vacuum chamber. Apressure of about 10⁻⁹ Pa is established in the vacuum chamber. Sodiumis then deposited on the sample using a zeolite source of the typemarketed by the SAES Getters Company, after having perfectly degassedthis source such that the pressure increase in the chamber during thedeposition does not exceed 3×10⁻⁹ Pa. The result is thus sodium clusterson the surface.

The deposition takes place at room temperature (about 25° C.) and the Nasource is placed at less than 10 cm from the sample, preferably at adistance of approximately 3 cm to 5 cm from this sample, the optimumdistance being about 3 cm.

The next step is annealings (at temperatures of a few hundred degrees,for example 350° C., during a time lasting from a few seconds to a fewminutes) of the β-SiC(100) 3×2 surface covered with sodium clusters.These annealings make it possible to optimise the number, size andposition of these clusters. They may be done using the Joule effect, bypassing an electrical current through the SiC sample and controlling itstemperature, for example using a pyrometer or a thermocouple.

In the examples given above, sodium was used to form the clusters.However, sodium could be replaced by other alkaline metals, andparticularly potassium, Cs, Rb or alkaline-earth metals, for examplesuch as Mg, Ca and Ba.

Furthermore, in these examples, an SiC substrate was used that in thecontext of this invention could be of the cubic or hexagonal type, richin Si and/or C. However, this substrate could be replaced by a diamondsubstrate or by a substrate made of a covalent semiconducting material,for example Si or Ge, or by a substrate made of an III-V compositesemiconducting material (for example GaAs, InP, GaSb, GaP or InAs) or anII-VI composite semiconducting material (for example CdTe, ZnO or ZnTe).

Furthermore, the low temperature thermal desorption mentioned above maybe used within a temperature range varying from room temperature (about25° C.) to the desorption temperature of the metal considered on thesubstrate considered.

The documents mentioned above are as follows:

[10] SiO₂-Si interface formation by catalytic oxidation using alkalimetals and removal of the catalyst

P. Soukiassian, T. M. Gentle, M. H. Bakshi and Z. Hurych

Journal of Applied Physics 60, 4339 (1986)

[11] Exceptionally large enhancement of InP(110) oxidation rate bycesium catalyst

P. Soukiassian, M. H. Bakshi and Z. Hurych

Journal of Applied Physics 61, 2679 (1987)

[12] Catalytic oxidation of semiconductors by alkali metals

P. Soukiassian, T. M. Gentle, M. H. Bakshi, A. S. Bommannavar and Z.Hurych

Physica Scripta (Sweden), 35, 757 (1987)

[13] Electronic promoters and semiconductor oxidation: alkali metals onSi(111)2×1 surface

A. Franciosi, P. Soukiassian, P. Philip, S. Chang, A. Wall, A. Raisanenand N. Troullier

Physical review B 35, Rapid Communication, 910 (1987)

[14] Si₃N₄-Si interface formation by catalytic nitridation using alkalimetals overlayers and removal of the catalyst: N2/Na/Si(100)2×1

P. Soukiassian, T. M. Gentle, K. P. Schuette, M. H. Bakshi and Z. Hurych

Applied Physics Letters 51, 346 (1987)

[15] Electronic properties of O₂ on Cs or Na overlayers adsorbed onSi(100)2×1 from room temperature to 650° C.

P. Soukiassian, M. H. Bakshi, Z. Hurych and T. M. Gentle

Physical Review B 35, Rapid Communication, 4176 (1987)

[16] Thermal growth of SiO₂-Si interfaces on a Si(111)7×7 surfacemodified by cesium

H. I. Starnberg, P. Soukiassian, M. H. Bakshi and Z. Hurych

Physical Review B 37, 1315 (1988)

[17] Alkali metal promoted oxidation of the Si(100)2×1 surface: coveragedependence and non-locality

H. I. Starnberg, P. Soukiassian and Z. Hurych

Physical Review B 39, 12775 (1989)

[18] Alkali metals and semiconductor surfaces: electronic, structuraland catalytic properties

P. Soukiassian and H. I. Starnberg (Guest Article)

in Physics and Chemistry of Alkali Metal Adsorption, Elsevier SciencePublishers B. V.,

Amsterdam, Netherlands, Materials Science Monographs 57, 449 (1989)

[19] Catalytic nitridation of a Il-V semiconductor using alkali metal

P. Soukiassian, T. Kendelewicz, H. I. Stamberg, M. H. Bakshi and Z.Hurych

Europhysics Letters 12, 87 (1990)

[20] Room temperature nitridation of gallium arsenide using alkali metaland molecular nitrogen

P. Soukiassian, H. I. Stamberg, T. Kendelewicz and Z. D. Hurych

Physical Review B 42, Rapid Communication 3769 (1990)

[21] Rb and K promoted nitridation of cleaved GaAs and InP surfaces atroom temperature

P. Soukiassian, H. I. Stamberg and T. Kendelewicz

Applied Surface Science 56, 772 (1992)

[22] Al₂O₃+x/Al interface formation by promoted oxidation using analkali metal and removal of the catalyst

Y. Huttel, E. Bourdié, P. Soukiassian, P. S. Mangat and Z. Hurych

Applied Physics Letters 62, 2437 (1993)

[23] Direct and Rb-promoted SiO_(x)/β-SiC(100) interface formation

M. Riehl-Chudoba, P. Soukiassian, C. Jaussaud and S. Dupont

Physical Review B 51, 14300 (1995).

1. A set of nano-objects (4, 10, 12, 22, 24), particularly atomicthreads, single dimensional nano-structures and quantum dots, this setbeing characterised in that the nano-objects are made of a metal and areformed on the surface (2, 6, 14) of a substrate made of amonocrystalline semiconducting material.
 2. A set of nano-objectsaccording to claim 1, in which the monocrystalline semiconductingmaterial is chosen from among monocrystalline silicon carbide,monocrystalline diamond, covalent monocrystalline semiconductors, andcomposite monocrystalline semiconductors.
 3. A set of nano-objectsaccording to claim 2, in which the substrate is a monocrystallinesubstrate of silicon carbide in the cubic phase.
 4. A set ofnano-objects according to claim 3, in which the surface (2) is a cubicsilicon carbide surface, rich in β-SiC (100) 3×2 silicon.
 5. A set ofnano-objects according to claim 1, in which the nano-objects arethree-dimensional clusters (4) of the metal on the surface.
 6. A set ofnano-objects according to claim 5, in which the clusters are distributedin an orderly manner on the surface and thus form a lattice of metaldots.
 7. A set of nano-objects according to claim 3, in which thesurface (6, 14) is a cubic silicon carbide surface which is Siterminated, β-SiC(100) c(4×2), and the nano-objects are parallel atomicthreads (10, 22) or parallel single-dimensional nanometric strips (12,24) of the metal.
 8. A set of nano-objects according to claim 7, inwhich the surface (6, 14) comprises parallel atomic threads (8, 20) ofSi, the atomic threads and single dimensional strips of the metal beingperpendicular to these atomic threads of Si.
 9. A set of nano-objectsaccording to claim 1, in which the surface comprises passivated areas(15) and non-passivated areas (16, 18) and the nano-objects are formedon these non-passivated areas of the surface.
 10. A set of nano-objectsaccording to claim 1, in which the metal is chosen from among metals forwhich the d band is full, jellium type metals, alkaline metals andtransition metals.
 11. A set of nano-objects according to claim 10, inwhich the metal is chosen from among sodium and potassium.
 12. Processfor making a set of nano-objects, in which a surface (2, 6, 14) of asubstrate made of a monocrystalline semiconducting material is prepared,and a metal is deposited on the surface thus prepared.
 13. Processaccording to claim 12, in which the monocrystalline semiconductingmaterial is chosen from among monocrystalline silicon carbide,monocrystalline diamond, covalent monocrystalline semiconductors andmonocrystalline composite semiconductors.
 14. Process according to claim13, in which the substrate is a monocrystalline substrate of siliconcarbide in the cubic phase.
 15. Process according to claim 12, in whichthe metal is deposited at a temperature greater than or equal to roomtemperature.
 16. Process according to claim 14, in which a surface (2)of cubic silicon carbide rich in silicon β-SiC(100) 3×2 is prepared, andthe metal is deposited on the surface thus prepared.
 17. Processaccording to claim 14, in which a silicon carbide surface (6,14) whichis Si terminated β-SiC(100) c(4×2) is prepared, the metal is depositedat room temperature on the surface thus prepared and, by surfacemigration of metal atoms along lines of Si—Si dimers of the surfacec(4×2), atomic threads of the metal are obtained that are parallel tothe lines of Si—Si dimers.
 18. Process according to claim 17, in which athermal annealing of the substrate is carried out at a temperature belowthe total desorption temperature of the metal.
 19. Process according toclaim 12, in which the metal is deposited by vacuum evaporation. 20.Process according to claim 12, in which the metal is deposited in aninert atmosphere.
 21. Process according to claim 12, in which passivatedareas (15) are formed on the thus prepared surface and the metal is thendeposited on non-passivated areas (16, 18) of this surface.
 22. Processaccording to claim 12, in which the metal is chosen from among metalsfor which the d band is full, jellium type metals, alkaline metals andtransition metals.
 23. Process according to claim 22, in which the metalis chosen from among sodium and potassium.
 24. Process according toclaim 17, in which a laser is used to obtain desorption of the metaleither by thermal interaction of the beam emitted by this laser over thesurface covered with metal, or by desorption of the metal induced byelectronic transitions.
 25. Process according to claim 14, in which thesurface is an sp type C terminated surface, namely the β-SiC(100) c(2×2)surface.
 26. Process according to claim 25, in which this surfacecomprises atomic lines of sp3 type C and atomic threads of metal areformed that are either parallel or perpendicular to the atomic lines ofC.
 27. Process according to claim 12, in which a lattice of metal dotsis formed on the surface of the substrate made of monocrystallinesemiconducting material, the substrate material located under the dotsis locally transformed and the lattice of dots is eliminated thus toobtain a super-lattice of dots made of the transformed material. 28.Process according to claim 27, in which the local transformation of thesubstrate material is chosen from among oxidation, nitridation andoxynitridation to obtain a super-lattice of dots made of the oxide,nitride or oxynitride of the material.
 29. Super-lattice of dots,obtained using the process according to claim 28, these dots being madeof the oxide, nitride or oxynitride of a monocrystalline semiconductingmaterial and formed at the surface of a substrate of this material.